This is a proposal for a comprehensive study of contextual influences on adolescent health and health behavior. Contextual influences include the influence of families, friends, romantic partners, peer networks, schools, neighborhoods, and communities. The data for the study are to be collected through questionnaires from a national sample of adolescents in grades 7 through 12, by the use of a school-based sampling design, followed by computer assisted home interviews with adolescents and their parents. These interviews will be followed by a second interview with respondents a year later. The proposal offers six integrated individual projects that capitalize on the unique strengths of the data set.